I'm going to pick up a 24-105 L and want to add a filter or cover for protection of the lens glass and secondarily as a possible UV filter. I don't want to get something that will affect the quality of the lens, can anyone recommend a good brand or is there a standard people use? Or am I just being paranoid?

I'm ruling out every possible problem so when I get bad pictures I know it's my fault.

A bad filter can make your image worse (e.g. flare) and a high quality coated one can make it better (e.g. haze). Look at the B+W 77mm UV Haze 010 F-Pro Filter.

And of course it will also, complete the weather sealing on the EF 24-105L.